Transfer credit from existing subscription

I've recently changed from a first Gen Ring to the 2020 Ring 2, and have been automatically given a free protect trial. I had an annual subscription for my previous device, which does not expire until Jan 27th. How do I replace my old device with my new one, on my current subscription.I spoke to one of your call takers, who had no clue, and simply told me to call back when my trial period ends.